The CB1 receptor is one of the most abundant neuromodulatory receptors in the brain, and is expressed at high levels in the hippocampus, cortex, cerebellum, and basal ganglia (e.g., Wilson et al., Science, 2002, vol. 296, 678-682). Selective CB1 receptor antagonists, for example pyrazole derivatives such as rimonabant (e.g., U.S. Pat. No. 6,432,984), can be used to treat various conditions, such as obesity and metabolic syndrome (e.g., Bensaid et al., Molecular Pharmacology, 2003 vol. 63, no. 4, pp. 908-914; Trillou et al., Am. J. Physiol. Regul. Integr. Comp. Physiol. 2002 vol. 284, R345-R353; Kirkham, Am. J. Physiol. Regul. Integr. Comp. Physiol. 2002 vol. 284, R343-R344), neuroinflammatory disorders (e.g., Adam, et al., Expert Opin. Ther. Patents, 2002, vol. 12, no. 10, 1475-1489; U.S. Pat. No. 6,642,258), cognitive disorders and psychosis (e.g., Adam et al., Expert Opin. Ther. Pat, 2002, vol. 12, pp. 1475-1489), addiction (e.g., smoking cessation; U.S. Patent Publ. 2003/0087933), gastrointestinal disorders (e.g., Lange et al., J. Med. Chem. 2004, vol. 47, 627-643) and cardiovascular conditions (e.g., Porter et al., Pharmacology and Therapeutics, 2001 vol. 90, 45-60; Sanofi-Aventis Publication, Bear Stearns Conference, New York, Sep. 14, 2004, pages 19-24).
There now exists extensive pre-clinical and clinical data supporting the use of CB1 receptor antagonists/inverse agonists for the treatment of obesity.
Preparations of marijuana (Cannabis sativa) have been used for over 5000 years for both medicinal and recreational purposes. The major psychoactive ingredient of marijuana has been identified as delta-9-tetrahydrocannabinol (delta-9-THC), one of a member of over 60 related cannabinoid compounds isolated from this plant. It has been demonstrated that delta-9-THC exerts its effects via agonist interaction with cannabinoid (CB) receptors. So far, two cannabinoid receptor subtypes have been characterised (CB1 and CB2). The CB1 receptor subtype is found predominantly in the central nervous system, and to a lesser extent in the peripheral nervous system and various peripheral organs. The CB2 receptor subtype is found predominantly in lymphoid tissues and cells. To date, three endogenous agonists (endocannabinoids) have been identified which interact with both CB1 and CB2 receptors (anandamide, 2-arachidonyl glycerol and noladin ether).
Genetically obese rats and mice exhibit markedly elevated endocannabinoid levels in brain regions associated with ingestive behaviour (Di Marzo et al. 2001 Nature 410: 822-825). Furthermore, increased levels of endocannabinoids are observed upon the fasting of normal, lean animals (Kirkham et al., British Journal of Pharmacology 2002, 136(4) 550-557).
Exogenous application of endocannabinoids leads to the same physiological effects observed with delta-9-THC treatment, including appetite stimulation (Jamshida et al., British Journal of Pharmacology 2001, 134: 1151-1 154), analgesia, hypolocomotion, hypothermia, and catalepsy.
CB1 (CB1−/−) and CB2 (CB2−/−) receptor knockout mice have been used to elucidate the specific role of the two cannabinoid receptor subtypes. Furthermore, for ligands such as delta-9-THC which act as agonists at both receptors, these mice have allowed identification of which receptor subtype is mediating specific physiological effects. CB1−/−, but not CB2−/−, mice are resistant to the behavioural effects of agonists such as delta-9-THC. CB1−/− animals have also been shown to be resistant to both the body weight gain associated with chronic high fat diet exposure, and the appetite-stimulating effects of acute food deprivation.
These findings suggest a clear role for both endogenous and exogenous cannabinoid receptor agonists in increasing food intake and body weight via selective activation of the CB1 receptor subtype.
The therapeutic potential for cannabinoid receptor ligands has been extensively reviewed (Exp. Opin. Ther. Pat. 1998, 8, 3010-313; Exp. Opin. Ther. Pat. 2000, 10, 1529-1538; Trends in Pharm. Sci. 2000, 2 1, 218-224; Exp. Opin. Ther. Pat. 2002, 12(10), 1475-1489).
At least one compound (SR-14171 6A; Rimonabant) characterised as a CB1 receptor antagonist/inverse agonist is known to be in clinical trials for the treatment of obesity.
Clinical trials with the CB1 receptor antagonist rimonabant have also observed an antidiabetic action that exceeds that accounted for by weight loss alone (Scheen A. J., et al., Lancet, 2006 in press). CB1 receptor mRNA is located on α- and β-cells in the Islets of Langerhans and it has been reported that CB1 receptor agonists reduce insulin release from pancreatic beta cells in vitro in response to a glucose load (Juan-Pico et al, Cell Calcium, 39, (2006), 155-162). Consistent with this, Bermudez-Siva et al., (Eur J Pharmacol., 531 (2006), 282-284) have reported that CB1 receptor agonists increase glucose intolerance following ip injection of a glucose load to rats. This effect was reversed by a CB1 receptor antagonist that increased glucose tolerance in the test when given alone. Thus, the action of rimonabant may be due to a direct action on the pancreas. It is also possible that CB1 receptor antagonists affect insulin sensitivity indirectly via an action on adiponectin (Chandran et al., Diabetes care, 26, (2003), 2442-2450) which is elevated by CB1 receptor antagonists (Cota et al., J Clin Invest., 112 (2003), 423-431; Bensaid et al., Mol Pharmacol., 63 (2003, 908-914). Indeed, it has been reported that endocannabinoid levels are enhanced in the pancreas and adipose tissue of obese and diabetic mice and in the plasma and adipose tissue of obese or type 2 diabetic patients (Matias et al., J Clin Endocrinol and Metab., 9 1 (2006), 3171-3180) suggesting a possible causal role of elevated cannabinoid tone in the onset of type 2 diabetes.
However, there is still a need for improved cannabinoid agents, particularly selective CB receptor antagonists, with fewer side-effects and improved efficacy.
WO 95125443, U.S. Pat. No. 5,464,788, and U.S. Pat. No. 5,756,504 describe N-aryl piperazine compounds useful for treating preterm labor, stopping labor, and dysmenorrhea. However, none of the N-aryl piperazines exemplified therein have an aryl and/or heteroaryl substituent at both the 1- and 2-positions of the piperazine ring.
WO 01/02372 and U.S. Published Application No. 200310186960 describe cyclized amino acid derivatives for treating or preventing neuronal damage associated with neurological diseases. However, none of the 3-aryl piperazine 2-ones exemplified therein have an aryl and/or heteroaryl substituent at both the 1- and 2-positions of the piperazine ring.
WO 96/01656 describes radiolabelled substituted piperazines useful in pharmacological screening procedures, including labeled N-aryl piperazines. However, none of the N-aryl piperazines exemplified therein have an aryl and/or heteroaryl substituent at both the 1- and 2-positions of the piperazine ring.
U.S. Pat. No. 5,780,480 describes N-aryl piperazines useful as fibrinogen receptor antagonists for inhibiting the binding of fibrinogen to blood platelets, and for inhibiting the aggregation of blood platelets. However, none of the N-aryl piperazines exemplified therein have an aryl and/or heteroaryl substituent at both the 1- and 2-positions of the piperazine ring.
WO 03/008559 describes choline analogs useful for treating conditions or disorders. However, the only substituted piperazine derivative exemplified is N-(2-hydroxyethyl)-N′-(2-pyridylmethyl)-piperazine.
JP 3-200758, JP 4-26683, and JP 4-364175 describe N,N′-diarylpiperazines (i.e., 1,4-diarylpiperazines) prepared by reacting bis(2-hydroxyethyl)arylamines with an amine such as aniline. However, no 1,2-disubstituted piperazines are exemplified.
WO 97122597 describes various 1,2,4-trisubstituted piperazine derivatives as tachykinin antagonists for treating tachykinin-mediated diseases such as asthma, bronchitis, rhinitis, cough, expectoration, etc. However, none of the 1,2,4-trisubstituted piperazine derivatives exemplified therein have an aryl and/or heteroaryl substituent at both the 1- and 2-positions of the piperazine ring.
EP 0268222, WO 88/01131, U.S. Pat. No. 4,917,896, and U.S. Pat. No. 5,073,544 describe compositions for enhancing the penetration of active agents through the skin, comprising azacyclohexanes, including N-acyl and N,N′-diacylpiperazines. However, none of the N-acyl or N,N′-diacylpiperazines exemplified therein have an aryl and/or heteroaryl substituent at both the 1- and 2-positions of the piperazine ring.
U.S. Pat. No. 6,528,529 describes compounds, including N,N′-disubstituted piperazines, which are selective for muscarinic acetylcholine receptors and are useful for treating diseases such as Alzheimer's disease. However, none of the N,N′-disubstituted piperazines exemplified therein have an aryl and/or heteroaryl substituent at both the 1- and 2-positions of the piperazine ring.
NL 6603256 describes various biologically active piperazine derivatives. However, none of the piperazine derivatives exemplified therein have a substituted aryl and/or heteroaryl substituent at both the 1- and 2-positions of the piperazine ring.
Wikström et al., J. Med. Chem. 2002, 45, 3280-3285, describe the synthesis of 1,2,3,4,10,14b-hexahydro-6-methoxy-2-methyldibnzo[c,f]pyrazine[1,2-a]azepin. However, none of the piperazine intermediates described therein have a substituted aryl and/or heteroaryl substituent at both the 1- and 2-positions of the piperazine ring.
WO 2007/018460 and WO 2007/018459 describe tricyclic piperidines and piperazine containing compounds, compositions, and methods for their use in treating obesity, psychiatric and neurological disorders. However, none of the compounds disclosed have a substituted aryl and/or heteroaryl substituent at both the 1- and 2-positions of a piperazine ring.
WO 2007/020502 describes pyrrolidone compounds as cannabinoid receptor ligands, in particular CB1 receptor ligands, and their use in treating diseases, conditions, and/or disorders modulated by cannabinoid receptor antagonists. However, none of the compounds disclosed have a substituted aryl and/or heteroaryl substituent at both the 1- and 2-positions of a piperazine ring.
WO 2007/057687 and W02006/060461 describe piperazine derivatives and their use as CB1 antagonists and in treating various diseases, conditions, and/or disorders modulated by cannabinoid receptor antagonists. However, there remains a need in the art for selective CB1 antagonists having a different functional group substitution pattern around the piperazine ring.